I'tikaf is the name of the voluntary Ramadan retreat in a mosque during the final days. A person observing i'tikaf remains in the mosque for worship, prayer, Quran reading, remembrance, and other permitted religious activities.
The retreat is especially associated with the final ten days of Ramadan because those nights are traditionally connected with seeking Laylat al-Qadr. Participants generally limit ordinary activities and leave the mosque only when necessary, according to the rules followed in their legal tradition.
I'tikaf is not the same as ihram, the ritual state entered for Hajj or Umrah. It is also distinct from ijtihad, the process of independent legal reasoning, and istikhara, a prayer for guidance.